Large-scale experimental study on pocket connections in GFRP-reinforced precast concrete frames

Abstract

This paper presents the results of an experimental study on a full-scale precast concrete frame reinforced with glass fibre reinforced polymer (GFRP) bars that was tested to failure under lateral cyclic loading. Within the frame four different pocket connections are tested that will lead to accelerated construction. Traditionally, a pocket connection is comprised of a column that is extended into a recessed portion of the connecting beam and the pocket is filled with grout to create a moment-resisting connection. In order to accelerate the construction process, quicker setting epoxy resin was used in place of grout. The results show that while the epoxy resin could significantly accelerate and simplify the construction procedure due to its workability in addition to its high early strength and non-shrinkable properties, its thickness and low modulus of elasticity significantly affected the performance of the pocket joint. The test frame showed a flag-shaped hysteretic behaviour with narrow loops and small residual displacement thus illustrating desirable frame self-centring behaviour. This self-centring behaviour was due to rocking of the column in the pocket connection. The frame displaced with a large displacement ductility of approximately 7.0, however, the level of energy dissipation and damping ratio was very low when compared with conventional concrete structures. This experimental study shows that pocket connections can be used for GFRP reinforced precast concrete elements, however, they should be designed carefully to account for the lower stiffness of GFRP reinforcement. Also, to avoid premature failure and achieve a higher capacity of the pocket connections, the material used in the pocket to fill the gap between column and beam is recommended to have higher strength and elastic modulus compared to the surrounding precast concrete.